Simulations of Electron Kinetics in Solar Wind Turbulence

Abstract

Solar wind plasma is a turbulent medium, with processes that operate on many scales. Observations below proton scales are rare. Future spacecraft missions will have the required resolution to make these observations, so theoretical experiments and simulations at these scales will become increasingly important in order to match observations to theory. In this thesis, kinetic simulations are used to study electron dynamics within a turbulent electron-proton plasma. Firstly in this thesis, a study of the formation of electron temperature anisotropy due to magnetic reconnection is presented using particle in cell (PIC) simulations of the turbulent decay of sub-proton scale fluctuations. A fluctuation power spectrum with approximately power law form down to scales of order the electron gyroradius is formed. The signatures of collisionless reconnection within the turbulent field are generally associated with regions of strong parallel electron temperature anisotropy. Electrons from spatially different locations, can mix at reconnection sites, generating multi-peaked velocity distribution functions, which could become unstable to further instabilities. This is evidence of an important role for reconnection in the dissipation of small scale turbulent fluctuations. Secondly, a new type of electron scale vortex is discussed, which can spontaneously form during the simulations of turbulence. These are generated by electrons in (quasi) trapped orbits, which diamagnetically reduce the local magnetic field, creating a coherent structure. The properties of these vortices are categorized and compared to observations of similar structures called “magnetic holes” observed within the Earth’s plasma sheet. Finally, we look to understand what dissipation is in a collisionless plasma. We examine signatures of dissipation in the previous simulations, and in simulations where electrostatic electron-electron beam modes are generated within the turbulence.